The proposed study will be conducted with the acetogenic bacteria Clostridium thermoaceticum, Clostridium thermoautotrophicum and Clostridium formicoaceticum. The important feature of these bacteria is their capacity to synthesize acetate from carbon dioxide. This occurs via a pathway, which is now recognized as a new autotrophic pathway of carbon dioxide fixation. It involves the reduction of carbon dioxide to formate by formate dehydrogenase and to carbon monoxide by carbon monoxide dehydrogenase. These enzymes contain tungsten, selenium and iron and nickel, zinc and iron, respectively. The role of these elements in the catalytic process will be studied using radioactive isotopes and spectrometric methods such as EPR, EXAFS, UV. The enzymes will be sequenced by cloning and DNA sequencing techniques to obtain binding sites for the metals and active sites on the enzymes. These studies will increase our understanding on how trace elements function in biological reaction catalyzed by enzymes. Formate is destined to form the methyl group of acetate. This involves several enzymes that are tetrahydrofolate- and vitamin B12-dependent. Sequencing and active site studies will be performed. These experiments will give knowledge about enzymes converting 1-carbon compounds, which are needed for DNA, RNA and protein synthesis. The acetogens when grown autotrophically must produce energy in a process involving the reduction of carbon dioxide. Several electron carriers including cytochrome b, ferredoxins, rubredoxins, and flavodoxins have been isolated from the acetogens. They also contain an ATP-ase. The possible involvement of these carriers in the electron transfer and ATP- generating processes will be studied. It is believed that these processes in the acetogens are primitive and the results would be of importance to interpret the evolution of energy producing biological systems.